In cardiovascular studies, in vivo or in vitro, changes in selected electrocardiographic (ECG) pa... more In cardiovascular studies, in vivo or in vitro, changes in selected electrocardiographic (ECG) parameters are monitored after various interventions to assess the basis of the origin and development of heart rhythm disorders. In vivo experiments are usually performed with the animals under general anesthesia what can mean that different anesthetics may have varying impact on myocardial electrophysiology immediately after administration of the anesthetic. Since normal, reference values of ECG parameters in non-anesthetized rats as well as their changes during the 24-hour period are not described in the literature, we summarized the presented values from the methodologies of studies that performed in vivo rat cardiovascular or toxicological experiments a search of the Web of Science database for articles published between 2000 and 2019; in total, 204 articles were retrieved. ECG parameters that were reported as baseline or control values were summarized and averages with ranges were calculated. It was surprising that, in some of these studies, neither the type of anesthesia or sex was reported. The data described below are average value, range and n = number of experiments from which values were evaluated, based on the type of general anesthesia-barbiturate (pentobarbital, phenobarbital, thiopental, nembutal); ketamine (ketamine/xylazine, medetomidine/ketamine, diazepam/ketamine); volatile (ether, isoflurane, desflurane) and urethane anesthesia. The HR varies depending on the type of general anesthesia, which can be problematic in evaluating changes in HR after an intervention. Other factors, in addition to general anesthesia that may directly or indirectly affect the initial HR can be , the time of day (active or inctive
General anaesthesia appears to disrupt cardiovascular stability by causing changes in cardiac fun... more General anaesthesia appears to disrupt cardiovascular stability by causing changes in cardiac function. The assessement of the chronobiological aspects of the pentobarbital anaesthesia impact on myocardial electrophysiology, acid-base balance and ion concentrations in a rat model was the aim of present study. The study was performed using pentobarbital-anaesthetized (40 mg/kg, intraperitoneal) female Wistar rats after adaptation to a 12h light : 12h dark (LD) cycle. Heart rate, rectal temperature, PQ interval, QT interval, QRS complex, QTc interval, and P, R and T wave amplitudes, acid-base balance and arterial concentrations of Na + , K + , Ca 2+ and Cl – were evaluated for their dependence on the LD cycle. LD differences were found in heart rate and rectal temperature measured before administration of the anaesthetic agent. Pentobarbital anaesthesia, however, eliminated LD differences in all electrophysiological parameters, parameters of acid-base balance and ion concentrations. LD differences with borderline statistical significance were found only for Na + levels, with a higher level in the light (ie, nonactive) period. Results of the present study suggest that pentobarbital is probably not the most suitable anaesthetic agent for chronobiological myocardial electrophysiological studies in rat models.
Objective: Respiratory alkalosis is an extremely common and complicated problem affecting virtual... more Objective: Respiratory alkalosis is an extremely common and complicated problem affecting virtually every organ system where the etiologies may be related to pulmonary or cardiovascular disorders. However, there are only few works describing daytime experiments or synchronization of animals to the external environmental periodicity. The aim of the study is to describe the circadian rhythm of the electrical stability of the heart under hyperventilatory conditions. Methods: Circadian rhythms of the electrical stability of the heart, measured by ventricular arrhythmia threshold ([VAT] measurement in 3 hour intervals), were followed during normal artificial ventilation (40 breaths/minute, tidal volume = 1 mL/100 g; n = 17) and hyperventilation (80 breaths/minute, tidal volume = 2 mL/100 g; n = 7) in pentobarbital (40 mg/kg administered intraperitoneally) anesthetized female Wistar rats, after 4 week adaptation on the light/ dark regime of 12 hour light/12 hour dark (40%-60% humidity, room temperature of 24°C in cages, two animals/cage with access to food and water ad libitum), with the dark period from 18.00h to 06.00h for 4 weeks.
Physiological research / Academia Scientiarum Bohemoslovaca
The circadian rhythm of ventricular fibrillation threshold (VFT) and its relation to the heart ra... more The circadian rhythm of ventricular fibrillation threshold (VFT) and its relation to the heart rate (HR) and the rectal temperature (RT) was studied in female Wistar rats. The animals were exposed to daily light-dark cycles of 12 h of light alternating with 12 h of darkness and were under pentobarbital anaesthesia (40 mg/kg i.p.). The experiments were performed on open chest animals and VFT was measured by direct stimulation of the myocardium. VFT in female rats showed a circadian rhythm with the acrophase -338 degrees (at 22.53 h), with the mesor 2.58 mA and the amplitude 0.33 mA. HR was not significantly changed during the experiments and no dependence was found between VFT and HR during the whole 24-hour period (r = 0.08). The acrophase of the circadian rhythm of HR (on -47 degrees, i.e. at 03.08 h) was shifted to the acrophase of VFT. The circadian rhythms of RT before the application of the anaesthetic agent and under general anaesthesia before the operative interventions had a...
A 24 h rhythm of the ventricular fibrillation threshold (VFT) was investigated in female Wistar r... more A 24 h rhythm of the ventricular fibrillation threshold (VFT) was investigated in female Wistar rats under conditions of normal ventilation (NV) (17 animals) and hypoventilation (HV) (10 animals). The animals were adapted to a daily 12:12 h light-dark cycle with the dark period from 18:00 to 06:00 under constant temperature conditions. The experiments were performed in pentobarbital anesthesia (40 mg/kg ip, open chest experiments) during the whole year, and the obtained results were averaged independently of the seasons. During NV, the VFT in female rats showed a significant 24 h rhythm (p < 0.01) with the mesor 2.59 +/- 0.53 mA, amplitude 0.33 +/- 0.11 mA, and acrophase -338 degrees (at 22:53 h) and the confidence intervals from -288 degrees to -7 degrees (from 19:12 to 00:28 h) using the population mean cosinor test. The maximal values of the VFT were measured in the active phase between 24:00 and 03:00 h. During HV, the rhythmicity of the VFT showed a more pronounced biphasic ...
Physiological research / Academia Scientiarum Bohemoslovaca
The aim of our study was to verify the relationship between heart rate (HR) and ventricular fibri... more The aim of our study was to verify the relationship between heart rate (HR) and ventricular fibrillation threshold (VFT) during different types of ventilation in female Wistar rats from the circadian point of view. The experiments were performed under pentobarbital anesthesia (40 mg/kg i.p., adaptation to a light-dark cycle 12:12 h, open chest experiments) and the obtained results were averaged independently of the seasons. The VFT measurements were performed during normal ventilation (17 animals) and hypoventilation (10 animals). The HR was recorded immediately before the rise of ventricular arrhythmias. Results are expressed as arithmetic means -/+ S.D. and differences are considered significant when p<0.05. The basic periodic characteristics were calculated using single and population mean cosinor tests. The results from our experiments have demonstrate that 1) the VFT and HR respond identically to hypoventilation by a decrease in the light and also in the dark phases, and 2) ...
To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes... more To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes in the electrical stability of the heart in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) and heart rate (HR) were measured in anesthetized female Wistar rats adapted to an LD regimen of 12 h:12 h (pentobarbital sodium 30 mg/kg, intraperitoneally, or ketamine/xylazine 100 mg/15 mg/kg, intramuscularly; open chest experiments) under artificial normoventilation (tidal volume 1 mL/100 g, respiratory rate 40 breaths/min) and during 20 min of hypoventilation (tidal volume 0.5 mL/100 g, respiratory rate 20 breaths/min) followed by 20 min of reoxygenation. Control and experimental groups were set according to LD cycle adaptation and type of anesthesia used: light control pentobarbital sodium group, n=67; dark control pentobarbital sodium group n=50; light hypoventilation-reoxygenation (hypo-reoxy) pentobarbital sodium group, n=26; dark hypo-reoxy pentobarbital s...
Erythrocyte microrheology changes were measured by cation-osmotic haemolysis in Wistar albino rat... more Erythrocyte microrheology changes were measured by cation-osmotic haemolysis in Wistar albino rats of both sexes. Erythrocyte membrane biophysical properties were estimated using the method of cation-osmotic haemolysis (COH) described by Nicak and Mojzis [Comp. Haematol. Int. 2 (1992), 84-86]. COH in male rats was higher in low ionic strength medium (spectrin skeleton) but without of statistical significance. The significantly higher COH in male rats in comparison with female rats was observed in higher ionic strength media. COH and erythrocyte deformability is also discussed. We suggest that changes in biophysical state of spectrin skeleton are followed by changes in lipid bilayer properties.
Hypoxia, similarly as myocardial ischemia, decreases the electric stability of the heart and thus... more Hypoxia, similarly as myocardial ischemia, decreases the electric stability of the heart and thus produces the conditions for the genesis of ventricular arrhythmias within the 24 h period however a prompt restoration of oxygen supply or blood flow within myocardium causes serious ventricular arrhythmias. Therefore the aim of our study was to evaluate the reoxygenation impact on myocardium after hypoventilation in circadian dependence. The experiments were performed in female Wistar rats (pentobarbital anesthesia 40 mg/1 kg i.p., open chest experiments). The animals were adapted to the light regimen 12:12 hours, with the dark phase from 18.00 h to 06.00 h. Normal ventilation was used in the control group (n = 17) and in the second one (n = 4), 20 min reoxygenation followed 20 min of hypoventilation. The heart rate (HR) had been recorded just before the ventricular arrhythmias rose. Hypoventilation decreased significantly (p < 0.001) the VFT and HR when compared with the control gr...
The aim of the study was to evaluate the effect of ventilatory manoeuvres on some ECG parameters ... more The aim of the study was to evaluate the effect of ventilatory manoeuvres on some ECG parameters as a function of the light-dark (LD) cycle in in vivo conditions. The PQ and QT intervals were measured in ketamine/xylazine-anaesthetized female Wistar rats (100 mg/15 mg/kg, i.m.) after adaptation to an LD cycle (12:12 h). The animals were exposed to a 2 min apneic episode and subsequent 20 min period of reoxygenation. Significant LD differences were found in the duration of the PQ interval (p < 0.001) after 30 and 60 sec., and in the QT interval after 90 (p < 0.01) and 120 sec. (p < 0.001), apneic episode. Reoxygenation restored the PQ and QT intervals with the preservation of LD differences from the pre-asphyxic period. It is concluded that although long-term asphyxia probably minimized LD differences in the duration of the PQ interval, the dispersion of refractory periods increases by the manner depending on LD cycle. Reoxygenation did not act proarrhythmogenicly and the fo...
Background / Purpose: It is supposed that both the hypoxic changes in the phasic and tonic drive ... more Background / Purpose: It is supposed that both the hypoxic changes in the phasic and tonic drive of the autonomic nervous system and the alterations in the sensitivity of the myocardium to the autonomic nervous drive maybe involved in the effect of preconditioning.This chronophysiological study was designed to examine the effect of a light-dark cycle adaptation on the heart rate responses, as a marker of autonomic drive, during cardiac preconditioning induced by repeated asphyxias in vivo. Main conclusion: The study showed that the cardiovascular responses have significant dependence on the light-dark cycle in the ketamine/xylazine paralyzed rats. Heart rate responses during the light part of the day clearly showed less pronounced dependence on the number of preconditioning cycles and exhibited less interindividual variability than in dark part of the day, particularly during the first half of the 20 minute hypoventilary challenge. This may suggest that preconditioning by 1-2 short ...
Physiological research / Academia Scientiarum Bohemoslovaca
Hypoventilation, as one of ventilatory disorders, decreases the electrical stability of the heart... more Hypoventilation, as one of ventilatory disorders, decreases the electrical stability of the heart similarly as ischemia. If preconditioning by short cycles of ischemia has a cardioprotective effect against harmful influences of a prolonged ischemic period, then preconditioning by hypoventilation (HPC) can also have a similar effect. Anesthetized rats (ketamine 100 mg/kg + xylasine 15 mg/kg i.m., open chest experiments) were subjected to 20 min of hypoventilation followed by 20 min of reoxygenation (control group). The preconditioning (PC) was induced by one (1PC), two (2PC) or three (3PC) cycles of 5-min hypoventilation followed by 5-min reoxygenation. The electrical stability of the heart was measured by a ventricular arrhythmia threshold (VAT) tested by electrical stimulation of the right ventricle. Twenty-minute hypoventilation significantly decreased the VAT in the control and 1PC groups (p<0.05) and non-significantly in 2PC vs. the initial values. Reoxygenation reversed the ...
Physiological research / Academia Scientiarum Bohemoslovaca
The aim of the study was to determine the dependence of changes in the electrical stability of th... more The aim of the study was to determine the dependence of changes in the electrical stability of the heart on the light-dark cycle (LD cycle) in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) was measured in female Wistar rats (adaptation to the light regime 12:12 h, ketamine/xylazine anesthesia 100 mg/15 mg/kg, i.m., open chest experiments). The conditions of the normal artificial ventilation and reoxygenation were V(T) = 1 ml/100 g, respiratory rate 40 breaths/min, hypoventilation V(T) = 0.5 ml/100 g, respiratory rate 20 breaths/min. The animals (n=11 light group; n=19 dark group) were subjected to 20 min hypoventilation followed by 20 min reoxygenation. The control prehypoventilatory VAT differences were not found between the light (1.90+/-0.84 mA) and dark (1.88+/-0.87 mA) part of the day. Artificial hypoventilation changed the VAT values in light and dark part of the day differently. While during the light period, the average VAT values in most ani...
In present time, to classify the healthy as potencional possibility of the organism to accept var... more In present time, to classify the healthy as potencional possibility of the organism to accept variable environment influences without the break of the biological important functions is not satisfactory. Examples from the different field of the clinical medicine refer to importance of the knowledge's of the circadian rhythmicity concerning many diseases, symptoms or significant remissions. Therefore, clinical trials considering the biological variability differ from the convectional studies by assumption that biology of patient is dynamic, that time of the diagnostic test running is significant and that drugs can influence safety and therapeutic effect in the dependence on the day-time. In paper, it is showed on some examples from the clinical practice that respection of the chronobiological principles may play the important role in the medical diagnostics as well as in therapy and may improve accuracy of the whatever functional examination. For terms, which are often used in the...
Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experi... more Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experiments. However, the chronobiological aspects of phenomenon of cardioprotection by hypoxic preconditioning have not been studied in in vitro and in vivo experiments, and there are no consistent data regarding the daytime dependence of preconditioning effects. To determine the protective effects of myocardial preconditioning applied during the dark (active) part of the day regimen, and to obtain an understanding concerning chronophysiological aspects of this phenomenon in in vivo rat experiments. The present study was designed to evaluate the effects of cardiac preconditioning induced by one to three cycles (1PC to 3PC) of asphyxia (5 min of artificial hypoventilation [tidal volume 0.5 mL/100 g of body weight, 20 breaths/min]) and reoxygenation (5 min of artificial ventilation [tidal volume 1 mL/100 g of body weight, 40 breaths/min]) on ventricular arrhythmia threshold (VAT) in the dark (a...
Physiological research / Academia Scientiarum Bohemoslovaca, Jan 12, 2013
Reoxygenation following hypoxic episodes can increase the risk for the development of ventricular... more Reoxygenation following hypoxic episodes can increase the risk for the development of ventricular arrhythmias, which, in addition to circadian aspects of reoxygenation arrhythmias has not been studied extensively. The aim of the present study was to evaluate circadian changes in the electrical stability of the rat heart during reoxygenation following a hypoventilatory episode. The electrical stability of the heart, defined in the present study as the ventricular arrhythmia threshold (VAT), was measured at 3 h intervals at clock times 09:00, 12:00, 15:00, 18:00, 21:00, 24:00, 03:00, 06:00 and 09:00 during 20 min hypoventilation (20 breaths/min, tidal volume = 0.5 ml/100 g body weight [n=17]) and subsequent 20 min reoxygenation (50 breaths/min, tidal volume = 1 ml/100 g body weight [n=4]) intervals. The experiments were performed using pentobarbital-anesthetized (40 mg/kg intraperitoneally) female Wistar rats that first underwent a four-week adaptation to a 12 h light:12 h dark regime...
To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes... more To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes in the electrical stability of the heart in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) and heart rate (HR) were measured in anesthetized female Wistar rats adapted to an LD regimen of 12 h:12 h (pentobarbital sodium 30 mg/kg, intraperitoneally, or ketamine/xylazine 100 mg/15 mg/kg, intramuscularly; open chest experiments) under artificial normoventilation (tidal volume 1 mL/100 g, respiratory rate 40 breaths/min) and during 20 min of hypoventilation (tidal volume 0.5 mL/100 g, respiratory rate 20 breaths/min) followed by 20 min of reoxygenation. Control and experimental groups were set according to LD cycle adaptation and type of anesthesia used: light control pentobarbital sodium group, n=67; dark control pentobarbital sodium group n=50; light hypoventilation-reoxygenation (hypo-reoxy) pentobarbital sodium group, n=26; dark hypo-reoxy pentobarbital s...
Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experi... more Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experiments. However, the chronobiological aspects of phenomenon of cardioprotection by hypoxic preconditioning have not been studied in in vitro and in vivo experiments, and there are no consistent data regarding the daytime dependence of preconditioning effects. To determine the protective effects of myocardial preconditioning applied during the dark (active) part of the day regimen, and to obtain an understanding concerning chronophysiological aspects of this phenomenon in in vivo rat experiments. The present study was designed to evaluate the effects of cardiac preconditioning induced by one to three cycles (1PC to 3PC) of asphyxia (5 min of artificial hypoventilation [tidal volume 0.5 mL/100 g of body weight, 20 breaths/min]) and reoxygenation (5 min of artificial ventilation [tidal volume 1 mL/100 g of body weight, 40 breaths/min]) on ventricular arrhythmia threshold (VAT) in the dark (a...
In cardiovascular studies, in vivo or in vitro, changes in selected electrocardiographic (ECG) pa... more In cardiovascular studies, in vivo or in vitro, changes in selected electrocardiographic (ECG) parameters are monitored after various interventions to assess the basis of the origin and development of heart rhythm disorders. In vivo experiments are usually performed with the animals under general anesthesia what can mean that different anesthetics may have varying impact on myocardial electrophysiology immediately after administration of the anesthetic. Since normal, reference values of ECG parameters in non-anesthetized rats as well as their changes during the 24-hour period are not described in the literature, we summarized the presented values from the methodologies of studies that performed in vivo rat cardiovascular or toxicological experiments a search of the Web of Science database for articles published between 2000 and 2019; in total, 204 articles were retrieved. ECG parameters that were reported as baseline or control values were summarized and averages with ranges were calculated. It was surprising that, in some of these studies, neither the type of anesthesia or sex was reported. The data described below are average value, range and n = number of experiments from which values were evaluated, based on the type of general anesthesia-barbiturate (pentobarbital, phenobarbital, thiopental, nembutal); ketamine (ketamine/xylazine, medetomidine/ketamine, diazepam/ketamine); volatile (ether, isoflurane, desflurane) and urethane anesthesia. The HR varies depending on the type of general anesthesia, which can be problematic in evaluating changes in HR after an intervention. Other factors, in addition to general anesthesia that may directly or indirectly affect the initial HR can be , the time of day (active or inctive
General anaesthesia appears to disrupt cardiovascular stability by causing changes in cardiac fun... more General anaesthesia appears to disrupt cardiovascular stability by causing changes in cardiac function. The assessement of the chronobiological aspects of the pentobarbital anaesthesia impact on myocardial electrophysiology, acid-base balance and ion concentrations in a rat model was the aim of present study. The study was performed using pentobarbital-anaesthetized (40 mg/kg, intraperitoneal) female Wistar rats after adaptation to a 12h light : 12h dark (LD) cycle. Heart rate, rectal temperature, PQ interval, QT interval, QRS complex, QTc interval, and P, R and T wave amplitudes, acid-base balance and arterial concentrations of Na + , K + , Ca 2+ and Cl – were evaluated for their dependence on the LD cycle. LD differences were found in heart rate and rectal temperature measured before administration of the anaesthetic agent. Pentobarbital anaesthesia, however, eliminated LD differences in all electrophysiological parameters, parameters of acid-base balance and ion concentrations. LD differences with borderline statistical significance were found only for Na + levels, with a higher level in the light (ie, nonactive) period. Results of the present study suggest that pentobarbital is probably not the most suitable anaesthetic agent for chronobiological myocardial electrophysiological studies in rat models.
Objective: Respiratory alkalosis is an extremely common and complicated problem affecting virtual... more Objective: Respiratory alkalosis is an extremely common and complicated problem affecting virtually every organ system where the etiologies may be related to pulmonary or cardiovascular disorders. However, there are only few works describing daytime experiments or synchronization of animals to the external environmental periodicity. The aim of the study is to describe the circadian rhythm of the electrical stability of the heart under hyperventilatory conditions. Methods: Circadian rhythms of the electrical stability of the heart, measured by ventricular arrhythmia threshold ([VAT] measurement in 3 hour intervals), were followed during normal artificial ventilation (40 breaths/minute, tidal volume = 1 mL/100 g; n = 17) and hyperventilation (80 breaths/minute, tidal volume = 2 mL/100 g; n = 7) in pentobarbital (40 mg/kg administered intraperitoneally) anesthetized female Wistar rats, after 4 week adaptation on the light/ dark regime of 12 hour light/12 hour dark (40%-60% humidity, room temperature of 24°C in cages, two animals/cage with access to food and water ad libitum), with the dark period from 18.00h to 06.00h for 4 weeks.
Physiological research / Academia Scientiarum Bohemoslovaca
The circadian rhythm of ventricular fibrillation threshold (VFT) and its relation to the heart ra... more The circadian rhythm of ventricular fibrillation threshold (VFT) and its relation to the heart rate (HR) and the rectal temperature (RT) was studied in female Wistar rats. The animals were exposed to daily light-dark cycles of 12 h of light alternating with 12 h of darkness and were under pentobarbital anaesthesia (40 mg/kg i.p.). The experiments were performed on open chest animals and VFT was measured by direct stimulation of the myocardium. VFT in female rats showed a circadian rhythm with the acrophase -338 degrees (at 22.53 h), with the mesor 2.58 mA and the amplitude 0.33 mA. HR was not significantly changed during the experiments and no dependence was found between VFT and HR during the whole 24-hour period (r = 0.08). The acrophase of the circadian rhythm of HR (on -47 degrees, i.e. at 03.08 h) was shifted to the acrophase of VFT. The circadian rhythms of RT before the application of the anaesthetic agent and under general anaesthesia before the operative interventions had a...
A 24 h rhythm of the ventricular fibrillation threshold (VFT) was investigated in female Wistar r... more A 24 h rhythm of the ventricular fibrillation threshold (VFT) was investigated in female Wistar rats under conditions of normal ventilation (NV) (17 animals) and hypoventilation (HV) (10 animals). The animals were adapted to a daily 12:12 h light-dark cycle with the dark period from 18:00 to 06:00 under constant temperature conditions. The experiments were performed in pentobarbital anesthesia (40 mg/kg ip, open chest experiments) during the whole year, and the obtained results were averaged independently of the seasons. During NV, the VFT in female rats showed a significant 24 h rhythm (p < 0.01) with the mesor 2.59 +/- 0.53 mA, amplitude 0.33 +/- 0.11 mA, and acrophase -338 degrees (at 22:53 h) and the confidence intervals from -288 degrees to -7 degrees (from 19:12 to 00:28 h) using the population mean cosinor test. The maximal values of the VFT were measured in the active phase between 24:00 and 03:00 h. During HV, the rhythmicity of the VFT showed a more pronounced biphasic ...
Physiological research / Academia Scientiarum Bohemoslovaca
The aim of our study was to verify the relationship between heart rate (HR) and ventricular fibri... more The aim of our study was to verify the relationship between heart rate (HR) and ventricular fibrillation threshold (VFT) during different types of ventilation in female Wistar rats from the circadian point of view. The experiments were performed under pentobarbital anesthesia (40 mg/kg i.p., adaptation to a light-dark cycle 12:12 h, open chest experiments) and the obtained results were averaged independently of the seasons. The VFT measurements were performed during normal ventilation (17 animals) and hypoventilation (10 animals). The HR was recorded immediately before the rise of ventricular arrhythmias. Results are expressed as arithmetic means -/+ S.D. and differences are considered significant when p<0.05. The basic periodic characteristics were calculated using single and population mean cosinor tests. The results from our experiments have demonstrate that 1) the VFT and HR respond identically to hypoventilation by a decrease in the light and also in the dark phases, and 2) ...
To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes... more To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes in the electrical stability of the heart in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) and heart rate (HR) were measured in anesthetized female Wistar rats adapted to an LD regimen of 12 h:12 h (pentobarbital sodium 30 mg/kg, intraperitoneally, or ketamine/xylazine 100 mg/15 mg/kg, intramuscularly; open chest experiments) under artificial normoventilation (tidal volume 1 mL/100 g, respiratory rate 40 breaths/min) and during 20 min of hypoventilation (tidal volume 0.5 mL/100 g, respiratory rate 20 breaths/min) followed by 20 min of reoxygenation. Control and experimental groups were set according to LD cycle adaptation and type of anesthesia used: light control pentobarbital sodium group, n=67; dark control pentobarbital sodium group n=50; light hypoventilation-reoxygenation (hypo-reoxy) pentobarbital sodium group, n=26; dark hypo-reoxy pentobarbital s...
Erythrocyte microrheology changes were measured by cation-osmotic haemolysis in Wistar albino rat... more Erythrocyte microrheology changes were measured by cation-osmotic haemolysis in Wistar albino rats of both sexes. Erythrocyte membrane biophysical properties were estimated using the method of cation-osmotic haemolysis (COH) described by Nicak and Mojzis [Comp. Haematol. Int. 2 (1992), 84-86]. COH in male rats was higher in low ionic strength medium (spectrin skeleton) but without of statistical significance. The significantly higher COH in male rats in comparison with female rats was observed in higher ionic strength media. COH and erythrocyte deformability is also discussed. We suggest that changes in biophysical state of spectrin skeleton are followed by changes in lipid bilayer properties.
Hypoxia, similarly as myocardial ischemia, decreases the electric stability of the heart and thus... more Hypoxia, similarly as myocardial ischemia, decreases the electric stability of the heart and thus produces the conditions for the genesis of ventricular arrhythmias within the 24 h period however a prompt restoration of oxygen supply or blood flow within myocardium causes serious ventricular arrhythmias. Therefore the aim of our study was to evaluate the reoxygenation impact on myocardium after hypoventilation in circadian dependence. The experiments were performed in female Wistar rats (pentobarbital anesthesia 40 mg/1 kg i.p., open chest experiments). The animals were adapted to the light regimen 12:12 hours, with the dark phase from 18.00 h to 06.00 h. Normal ventilation was used in the control group (n = 17) and in the second one (n = 4), 20 min reoxygenation followed 20 min of hypoventilation. The heart rate (HR) had been recorded just before the ventricular arrhythmias rose. Hypoventilation decreased significantly (p < 0.001) the VFT and HR when compared with the control gr...
The aim of the study was to evaluate the effect of ventilatory manoeuvres on some ECG parameters ... more The aim of the study was to evaluate the effect of ventilatory manoeuvres on some ECG parameters as a function of the light-dark (LD) cycle in in vivo conditions. The PQ and QT intervals were measured in ketamine/xylazine-anaesthetized female Wistar rats (100 mg/15 mg/kg, i.m.) after adaptation to an LD cycle (12:12 h). The animals were exposed to a 2 min apneic episode and subsequent 20 min period of reoxygenation. Significant LD differences were found in the duration of the PQ interval (p < 0.001) after 30 and 60 sec., and in the QT interval after 90 (p < 0.01) and 120 sec. (p < 0.001), apneic episode. Reoxygenation restored the PQ and QT intervals with the preservation of LD differences from the pre-asphyxic period. It is concluded that although long-term asphyxia probably minimized LD differences in the duration of the PQ interval, the dispersion of refractory periods increases by the manner depending on LD cycle. Reoxygenation did not act proarrhythmogenicly and the fo...
Background / Purpose: It is supposed that both the hypoxic changes in the phasic and tonic drive ... more Background / Purpose: It is supposed that both the hypoxic changes in the phasic and tonic drive of the autonomic nervous system and the alterations in the sensitivity of the myocardium to the autonomic nervous drive maybe involved in the effect of preconditioning.This chronophysiological study was designed to examine the effect of a light-dark cycle adaptation on the heart rate responses, as a marker of autonomic drive, during cardiac preconditioning induced by repeated asphyxias in vivo. Main conclusion: The study showed that the cardiovascular responses have significant dependence on the light-dark cycle in the ketamine/xylazine paralyzed rats. Heart rate responses during the light part of the day clearly showed less pronounced dependence on the number of preconditioning cycles and exhibited less interindividual variability than in dark part of the day, particularly during the first half of the 20 minute hypoventilary challenge. This may suggest that preconditioning by 1-2 short ...
Physiological research / Academia Scientiarum Bohemoslovaca
Hypoventilation, as one of ventilatory disorders, decreases the electrical stability of the heart... more Hypoventilation, as one of ventilatory disorders, decreases the electrical stability of the heart similarly as ischemia. If preconditioning by short cycles of ischemia has a cardioprotective effect against harmful influences of a prolonged ischemic period, then preconditioning by hypoventilation (HPC) can also have a similar effect. Anesthetized rats (ketamine 100 mg/kg + xylasine 15 mg/kg i.m., open chest experiments) were subjected to 20 min of hypoventilation followed by 20 min of reoxygenation (control group). The preconditioning (PC) was induced by one (1PC), two (2PC) or three (3PC) cycles of 5-min hypoventilation followed by 5-min reoxygenation. The electrical stability of the heart was measured by a ventricular arrhythmia threshold (VAT) tested by electrical stimulation of the right ventricle. Twenty-minute hypoventilation significantly decreased the VAT in the control and 1PC groups (p<0.05) and non-significantly in 2PC vs. the initial values. Reoxygenation reversed the ...
Physiological research / Academia Scientiarum Bohemoslovaca
The aim of the study was to determine the dependence of changes in the electrical stability of th... more The aim of the study was to determine the dependence of changes in the electrical stability of the heart on the light-dark cycle (LD cycle) in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) was measured in female Wistar rats (adaptation to the light regime 12:12 h, ketamine/xylazine anesthesia 100 mg/15 mg/kg, i.m., open chest experiments). The conditions of the normal artificial ventilation and reoxygenation were V(T) = 1 ml/100 g, respiratory rate 40 breaths/min, hypoventilation V(T) = 0.5 ml/100 g, respiratory rate 20 breaths/min. The animals (n=11 light group; n=19 dark group) were subjected to 20 min hypoventilation followed by 20 min reoxygenation. The control prehypoventilatory VAT differences were not found between the light (1.90+/-0.84 mA) and dark (1.88+/-0.87 mA) part of the day. Artificial hypoventilation changed the VAT values in light and dark part of the day differently. While during the light period, the average VAT values in most ani...
In present time, to classify the healthy as potencional possibility of the organism to accept var... more In present time, to classify the healthy as potencional possibility of the organism to accept variable environment influences without the break of the biological important functions is not satisfactory. Examples from the different field of the clinical medicine refer to importance of the knowledge's of the circadian rhythmicity concerning many diseases, symptoms or significant remissions. Therefore, clinical trials considering the biological variability differ from the convectional studies by assumption that biology of patient is dynamic, that time of the diagnostic test running is significant and that drugs can influence safety and therapeutic effect in the dependence on the day-time. In paper, it is showed on some examples from the clinical practice that respection of the chronobiological principles may play the important role in the medical diagnostics as well as in therapy and may improve accuracy of the whatever functional examination. For terms, which are often used in the...
Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experi... more Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experiments. However, the chronobiological aspects of phenomenon of cardioprotection by hypoxic preconditioning have not been studied in in vitro and in vivo experiments, and there are no consistent data regarding the daytime dependence of preconditioning effects. To determine the protective effects of myocardial preconditioning applied during the dark (active) part of the day regimen, and to obtain an understanding concerning chronophysiological aspects of this phenomenon in in vivo rat experiments. The present study was designed to evaluate the effects of cardiac preconditioning induced by one to three cycles (1PC to 3PC) of asphyxia (5 min of artificial hypoventilation [tidal volume 0.5 mL/100 g of body weight, 20 breaths/min]) and reoxygenation (5 min of artificial ventilation [tidal volume 1 mL/100 g of body weight, 40 breaths/min]) on ventricular arrhythmia threshold (VAT) in the dark (a...
Physiological research / Academia Scientiarum Bohemoslovaca, Jan 12, 2013
Reoxygenation following hypoxic episodes can increase the risk for the development of ventricular... more Reoxygenation following hypoxic episodes can increase the risk for the development of ventricular arrhythmias, which, in addition to circadian aspects of reoxygenation arrhythmias has not been studied extensively. The aim of the present study was to evaluate circadian changes in the electrical stability of the rat heart during reoxygenation following a hypoventilatory episode. The electrical stability of the heart, defined in the present study as the ventricular arrhythmia threshold (VAT), was measured at 3 h intervals at clock times 09:00, 12:00, 15:00, 18:00, 21:00, 24:00, 03:00, 06:00 and 09:00 during 20 min hypoventilation (20 breaths/min, tidal volume = 0.5 ml/100 g body weight [n=17]) and subsequent 20 min reoxygenation (50 breaths/min, tidal volume = 1 ml/100 g body weight [n=4]) intervals. The experiments were performed using pentobarbital-anesthetized (40 mg/kg intraperitoneally) female Wistar rats that first underwent a four-week adaptation to a 12 h light:12 h dark regime...
To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes... more To determine the effect of the light-dark cycle (LD) and type of anesthetic agent used on changes in the electrical stability of the heart in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) and heart rate (HR) were measured in anesthetized female Wistar rats adapted to an LD regimen of 12 h:12 h (pentobarbital sodium 30 mg/kg, intraperitoneally, or ketamine/xylazine 100 mg/15 mg/kg, intramuscularly; open chest experiments) under artificial normoventilation (tidal volume 1 mL/100 g, respiratory rate 40 breaths/min) and during 20 min of hypoventilation (tidal volume 0.5 mL/100 g, respiratory rate 20 breaths/min) followed by 20 min of reoxygenation. Control and experimental groups were set according to LD cycle adaptation and type of anesthesia used: light control pentobarbital sodium group, n=67; dark control pentobarbital sodium group n=50; light hypoventilation-reoxygenation (hypo-reoxy) pentobarbital sodium group, n=26; dark hypo-reoxy pentobarbital s...
Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experi... more Cardioprotective effects by hypoxic preconditioning are well known mainly through in vitro experiments. However, the chronobiological aspects of phenomenon of cardioprotection by hypoxic preconditioning have not been studied in in vitro and in vivo experiments, and there are no consistent data regarding the daytime dependence of preconditioning effects. To determine the protective effects of myocardial preconditioning applied during the dark (active) part of the day regimen, and to obtain an understanding concerning chronophysiological aspects of this phenomenon in in vivo rat experiments. The present study was designed to evaluate the effects of cardiac preconditioning induced by one to three cycles (1PC to 3PC) of asphyxia (5 min of artificial hypoventilation [tidal volume 0.5 mL/100 g of body weight, 20 breaths/min]) and reoxygenation (5 min of artificial ventilation [tidal volume 1 mL/100 g of body weight, 40 breaths/min]) on ventricular arrhythmia threshold (VAT) in the dark (a...
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Papers by Pavol Svorc